This invention generally relates to blow molding methods and machines for producing heat set plastic containers. More specifically, this invention relates to a mechanism which stabilizes a blow molded plastic container in the blow mold cavity.
Stretch blow molding processes are performed in automatic machines which sequence preforms and containers through several stations to complete the bottle fabrication process. The blow molding operation is performed with a plastic preform which is inflated with a gas to form a container. If the container becomes unstable or hung up in the mold during demolding, the machine must be shut down and the operator must remove the obstructing container from the machine. This results in costly lost production time and an increase in the overall machine cycle time for each container. This is economically undesirable. The trend is to reduce the cycle time of each operation in the cycle. By increasing the speed of the operation, there is a greater possibility of losing control of a container during extraction from the mold because of the high acceleration rates of the various machine components.
When the container is in the finish portion down orientation, there is a tendency for some types of containers to hang up or jam in the stretch blow molding station because of a loss of control of the container during the demolding process.
Containers with a complex sidewall geometry or a high aspect ratio are particularly prone to adhering to one side of the mold as the mold is opened. The result is that the container can cock relative to the mandrel while the container is being removed from the mold. The mandrel is part of the core assembly which passes through the finish portion and into the container. When a container cocks on the mandrel, it can jam in the mold due to the loss of control of the orientation of the bottle. Another aspect of the problem relates to containers with dimensional variations in the inside diameter of the finish portion. If the inside diameter of the finish portion is too large, the container can fall off the mandrel as a result of being jostled by the mold opening which can result in the container being jammed in the mold.
On many rotary type blow molding machines, a mechanism integral with the machine grips and stabilizes the container during demolding, preventing the problems described above. On linear type machines, a bottle stabilizer is not integral with the molding machine. Thus, there is a need for a container stabilizing device applicable to linear molding machines, with preforms in a threads or finish portion down orientation, which prevents the mold opening action from destabilizing the container relative to the mandrel thus preventing the container from getting hung up or jamming in the mold.
The present invention provides a blow molding device which is adapted for stabilizing a container formed from a preform. The container and preform each have a portion defining a finish. The device includes a mold having a first mold section, a second mold section and a cavity therebetween. The first mold section is movable toward and away from the second mold section. A mandrel is adjacent to the mold. The mandrel has one of the preform and the container disposed thereon. The first mold section and the second mold section is adapted to open and close about the mandrel in order to permit the mandrel to move into and out of the cavity in the mold. At least one jaw is adjacent to one of the first mold section and the second mold section. The at least one jaw conforms to the finish and moves transversely of the finish. The at least one jaw is biased by a resilient member to compress the finish of the preform and the bottle to the mandrel to stabilize the container when the first mold section and the second mold section move away from one another.
No complex controls or actuators are required for the operation of the present invention. When the mold is fully opened, the at least one jaw disengages from the finish of the container and allows for the passage of the incoming mandrel and clamping device, the preform, the outgoing mandrel and clamping device, and finally the molded container. As the mold closes, each jaw comes into contact with the preform finish. Upon further closing of the mold, the jaws travel on guides to compress springs and grip the preform finish. After mold closure and the blow molding process, the spring loaded jaws continue to grip the container finish and retain the container""s position relative to the mandrel as the mold initially opens. As the mold further opens, the jaws continue to contact the container finish by the bias of the springs until the jaws reach the end of their travel on the guide rods, and move with each of the mold sections during the remainder of the mold opening travel. Thus, the operation of the present invention is mechanically sequenced with the normal mold opening and closing procedure.
Further features and advantages of the invention will become apparent from the following discussion and accompanying drawings.